Can hCG levels rise to a point where you no longer test positive on an HPT?

[Jaimee]

So this is a hypothesis that has come up in some past posts and I even read an article that referenced high hCG levels affecting HPT results called the "hook effect." 

Very high concentrations of hCG could swamp the binding sites of both antibodies used in these kits so that little or no hCG is captured in the test area. Therefore a test would appear negative despite high concentrations of hCG being present.

....

Manufacturers have quoted hCG concentrations of >250,000IU/L at 8-10 weeks. Multiple pregnancies and hCG secreting tumours can produce even higher concentrations of hCG but this is a rare occurrence. Although most urine samples screened for pregnancy are collected a short time after the last missed period, women will occasionally wait several weeks before testing for pregnancy - when the hCG concentrations will be very high. We tested the reliability of the devices up to 500,000IU/L. Eight devices gave a weak positive at this concentration although a strong positive at 100,000IU/L. This indicated that these devices suffered from some hook effect. At this high concentration all results were seen as positive and therefore indicate pregnancy, but the signal would be even weaker or absent at higher concentrations.

I am currently 27w5d pregnant.  While I have no idea what my hCG levels are at this point, I do know that they were 68,870 at 9 weeks.  According to the American Pregnancy Association, hCG levels tend to peak between 8 and 11 weeks, decline, and then remain level for the remainder of pregnancy.  So I can probably make the assumption that my levels are less than 68,870 at this point and therefore not high enough to cause the hook effect described above.

I was curious and had an extra FRER laying around that was going to expire anyway.  So I tested today (with SMU) and got an obvious positive result.  But I will say that it was not as quick to show up or as dark as my positive result at 20 DPO.  I venture to say that most women would have low enough hCG levels to test positive the entirety of their pregnancies.

Anyone else want to join in the experiment?